Start The new Workbench prefs. Locate PC0 and change it
to 'Show only when valid' or something like that.
Save your settings.
Check if ghostbuster is in wbstartup and reboot.
Insert an amiga floppy and check if PC0:

still shows up.
If not, then installation was succesfull.
If it still shows, then recheck everything I said.
Regards,
Lloyd